Drug overdose is the single greatest cause of mortality among injection drug users (IDUs) in the U.S. Fatal heroin overdoses cause more than half of all deaths among IDUs, which far exceeds the proportion of deaths due to AIDS or other causes. Administration of heroin or other opiods via intravenous route not only increases the risk for HIV and other blood-borne pathogens, but also significantly increases the risk a of potentially fatal overdose. Therefore, IDUs are a population at elevated risk for both HIV infection and fatal drug overdose. A heroin overdose can be safely reversed with the administration of naloxone (brand name Narcan) - a legal, nonscheduled opioid antagonist. Naloxone is currently prescribed and distributed by overdose prevention programs (OPP) in 15 states. Despite the common-sense notion that these programs "work," scientifically designed evaluations of OPPs are almost non-existent, and outcomes are still poorly defined. The proposed study is designed to investigate changes in overdose response and other drug-related health behaviors among IDUs participating in two OPPs in Los Angeles. The study will address the following three specific aims: observe changes in overdose response behavior among IDUs;examine whether participating in overdose prevention training or overdose response (i.e. performing a "rescue") affects other drug-related health behaviors;and investigate structural, social, and psychological barriers towards enrolling IDUs into OPPs. The proposed study will use qualitative and quantitative methods to study samples of IDUs recruited from two community-based programs in Los Angeles that conduct overdose prevention training - Homeless Health Care Los Angeles (HHCLA) and Common Ground (CG). Quantitative baseline and "incident report" data will be collected as part of an existing protocol started in November, 2008, to document behaviors in response to witnessed overdoses and circumstances precipitating requests for refills of naloxone. Qualitative in-depth interviews with 150 IDUs (100 trained and 50 untrained) will explore rationales for and barriers to enrolling in overdose prevention training, the effects of training participation, differences between training programs, and the effects of participating in an overdose rescue. PUBLIC HEALTH RELEVANCE: The proposed study will fill a critical gap in the public health literature on opioid overdose and the effects of OPPs among IDUs, who are at elevated risk for death due to overdose. Additionally, the study will provide important information about how the effects of participating in overdose prevention training and practicing prevention skills may be associated with non-overdose related health behaviors, such as HIV risk behavior.